Can someone explain to me the differents between 20 melt PP and 35melt?I've made some parts with 20 melt and they turned out great. But if Igive the living hinge a twist she breaks.Would I get a non tearing living hinge with 35 melt?

In absence of other information, I have to assume that 20 melt means a meltflow of 20 g/10 minutes, and 35 melt means a melt flow of 35 g/10 minutes.In other words, the 20 melt flow flows less, that is, the 20 melt is moreviscous than the 35 melt resin. Assuming similar molecular weightdistribution for the two resin, the more viscous 20 melt flow should have ahigher molecular weight than the 35 melt flow. Higher molecular weightresin of 20 melt flow is likely to be tougher than the lower molecularweight 35.

But, the above assumes that the two resins are identical in all respectexcept for melt flow (ask your resin supplier!). Furthermore, if yourmolding conditions are marginal, (not enough packing pressure, time,temperature) the 35 melt flow may give you better results than the 20 meltflow resin.

Is the hinge a proven design? Are there notches or other stress risers inthe part? Your resin supplier may be able to provide you with known designsfor hinges.

Thanks Ernie for the reply. The living hinge functions great.It's onlywhen I twist it, then it fails. If I try to pull it straight apartit's very strong, like trying to snap twine. I think the design isgood. A sales person told me that it would be more tear resistant if Iran 35 melt. There's no notching, she folds nicely. I even baked it at160 degrees and the hinge didn't fail. Am I being to critical?

If your hinges break already during their very first use, you may havechosen the wrong plastic and you ought to consider the use of H-POM insteadof PP. If the hinge gets only used once during the lifetime of the part, ahigh-molecular (low MFI) grade of PP may eventually work, assuming thedesign of your part & hinge are correct, but if the hinge gets usedfrequently PP is perhaps not the right choise of material. With any plasticyou must also assure that optimal molding conditions are used ...